JP2014215206A5 - - Google Patents

Description

Then, by performing a thermal acid reduction, silicon oxide film is formed in a portion where the silicon nitride film is removed. Thereby, a relatively thick silicon oxide film is formed on the surfaces of the first well region 12 and the third well region 14, and then the silicon nitride film is removed. Next, n-type impurities (for example, phosphorus) for forming the second well region 13 (see FIG. 1) of the MOS region are implanted using the relatively thick silicon oxide film as an implantation mask.

In this way, as shown in FIG. 2, the field oxide film 19 is formed in the pressure sensor region 16, and the field oxide films 15 and 19 are formed in the MOS region 17. The thickness of the field oxide films 15 and 19 is about 0.2 to 1.0 μm. Note that the remaining underlying oxide film 21 is located at the position where the silicon nitride film is removed. A semiconductor element such as a MOS transistor formed in a region defined by the field oxide films 15 and 19 is electrically insulated by the field oxide films 15 and 19 and a channel stopper 20 formed immediately below the field oxide films 15 and 19. . Thereafter, the underlying oxide film 21 is removed.

In the semiconductor pressure sensor described above, by opening the surface side of the movable electrode 39 in the pressure sensor region 16 to the external space through the opening 54, the movable electrode 39 is displaced corresponding to the external pressure, and the fixed electrode The distance (gap) between 23 b and the movable electrode 39 changes. In the semiconductor pressure sensor, the pressure value is measured by detecting the change in the interval as the change in the capacitance value. Further, by setting the pressure in the vacuum chamber 51 located directly below the movable electrode 39 as a reference pressure, this semiconductor pressure sensor can function as an absolute pressure sensor.

That is, the semiconductor pressure sensor described above, a pressure sensor of capacitive measuring changes in capacitance as the pressure value, the capacitance value, the change of the capacitance value changes in the distance between the fixed electrode 23 b and the movable electrode 39 As the pressure is measured. More precisely, the capacitance values (capacitance value A and capacitance value) of the first fixed electrode protective film 25b and the second fixed electrode protective film 27b located between the fixed electrode 23b and the vacuum chamber 51 are more accurately described. B) The capacitance value (capacitance value C) of the oxide films 35 and 38 positioned between the movable electrode 39 and the vacuum chamber 51 and the capacitance value (total value) of the vacuum chamber 51 (capacitance value D). Value). Among these, the capacity is changed only by the capacity value D of the vacuum chamber 51 due to the external pressure. Therefore, in order to measure the pressure value more accurately, the initial capacity values of the capacity values A to C ( It is necessary to accurately grasp the initial value.

Further, the sacrificial film 30d in the pressure sensor region 16 is simultaneously the same in the step of forming the gate electrode 30a of the p-channel type MOS transistor, the gate electrode 30b of the n-channel type MOS transistor, and the gate electrode 30c of the EPROM in the MOS region 17. Formed from material. The relationship between these processes means that a dedicated process for forming the pressure sensor is unnecessary.